1. Field of the Invention
This invention relates to a process for producing a light-receiving member, a light-receiving member produced by the method, an electrophotographic apparatus having the light-receiving member, and an electrophotographic method using the light-receiving member. More particularly, it relates to a process for producing a light-receiving member that has a superior cleaning performance and can obtain high-quality images free of faint images and smeared images in any environment, an electrophotographic apparatus having the light-receiving member, and an electrographic method using the light-receiving member.
2. Related Background Art
As materials for light-receiving members to be used in electrophotographic photosensitive members, inorganic materials such as selenium, cadmium sulfide, zinc oxide and amorphous silicon (hereinafter referred to as "a-Si") and organic materials are proposed in variety. Of these, non-single-crystalline deposited films containing silicon atoms as a main component, typified by a-Si, have been proposed as materials for photosensitive members having a high performance and a high durability and free from environmental pollution, as exemplified by amorphous deposited films of a-Si containing hydrogen and/or a halogen such as fluorine or chlorine (e.g., hydrogen or halogen compensates dangling bonds). Some of these have been put into practical use.
U.S. Pat. No. 4,265,991 discloses a technique concerning an electrophotographic photosensitive member comprising a photoconductive layer mainly formed of a-Si.
Such a-Si type photosensitive members typified by a-Si have advantages that they have a high surface hardness, exhibit a high sensitivity to long-wavelength light of semiconductor lasers (770 nm to 800 nm) or the like and also are almost free from deterioration due to repeated use. Hence, they are put into wide use in photosensitive members for electrophotographic apparatus as exemplified by high-speed copying machines and LBPs (laser beam printers).
As processes for forming such silicon type non-single-crystalline deposited films, a number of processes are known in the art, as exemplified by sputtering, a process in which a material gas is decomposed by heat (thermal CVD), a process in which a material gas is decomposed by light (optical CVD), and a process in which a material gas is decomposed by plasma (plasma-assisted CVD). In particular, plasma-assisted CVD, i.e., a process in which a material gas is decomposed by glow discharge or the like generated by utilizing a direct current, a high-frequency (RF or VHF) or a microwave to form a deposited film on any desired substrate such as glass, quartz, heat-resistant synthetic resin film, stainless steel or aluminum is being widely put into practical use not only in the process for forming amorphous-silicon deposited films for use in electrophotography but also in processes for forming deposited films for other uses. Apparatuses therefor are also proposed in a wide variety.
In recent years, taking into account its application in electrophotographic photosensitive members, it is strongly sought to improve film quality and processability, and various measures are studied to do so.
In particular, a plasma-assisted process making use of high-frequency power is widely used because of its various advantages such that it has a high discharge stability and can be used to form insulating materials such as oxide films and nitride films.
Incidentally, in recent years, plasma-assisted CVD carried out at a high frequency of 20 MHz or above using a parallel flat plate type plasma-assisted .CVD apparatus, as reported in Plasma Chemistry and Plasma Processing, Vol. 7, No. 3 (1987), pp.267-273, has attracted notice, which shows a possibility of improving the deposition rate without a lowering of the performance of deposited films by making the discharge frequency higher than 13.56 MHz conventionally used. Making the discharge frequency higher in this way is also reported in respect of sputtering, and has been widely studied in recent years.
Now, as charging and charge-eliminating means of conventional light-receiving members of various types including a-Si light-receiving members, a corona assembly (corotron, scorotron) is used which comprise a wire electrode (e.g., a metal wire such as a tungsten wire of 50 to 100 .mu.m diameter, coated with gold) and a shielding plate in almost all cases. More specifically, corona electric currents generated by applying a high voltage (about 4 to 8 kV) to the wire electrode of the corona assembly are made to act on the surface of the light-receiving member to charge the surface of the light-receiving member and eliminate charges therefrom. The corona assembly is superior in uniform charging and charge elimination.
However, corona discharge is accompanied by generation of ozone (O.sub.3) in a fairly large quantity. The generated ozone oxidizes nitrogen in the air to produce nitrogen oxides (NO.sub.x). The nitrogen oxides thus produced further react with water in the air to produce nitric acid and the like. The products produced by corona discharge (hereinafter referred to as "corona discharge products") such as nitrogen oxides and nitric acid may adhere to and deposit on the light-receiving member and its surrounding machinery to contaminate their surfaces. Such corona discharge products have so strong a moisture absorption that the light-receiving member surface having adsorbed them exhibits a low resistance because of the moisture absorption of the corona discharge products having adhered thereto, so that the ability of charge retention may substantially lower on the whole or in part to cause faulty images such as faint images and smeared images (a state in which the charges on the surface of the light-receiving member leak in the surface direction to cause deformation, or no formation, of patterns of electrostatic latent images).
Corona discharge products having adhered to the inner surface of the shielding plate of the corona assembly evaporate and become liberated not only while the electrophotographic apparatus is operating but also while the apparatus is not operating, e.g., at night. The corona discharge products having thus evaporated and become liberated adhere to the surface of the light-receiving member at its part corresponding to the discharge opening of the corona assembly to cause further moisture absorption. Hence, the surface of the light-receiving member may have a low resistance. Thus, the first copy initially outputted when the apparatus is again operated after inactivation, or copies on several sheets subsequent thereto, tend(s) to have faint images or smeared images occurring at the area corresponding to the opening of the corona assembly. This tends to occur especially when the corona assembly is an AC corona assembly. Moreover, in the case when the light-receiving member is an a-Si type light-receiving member, the faint images or smeared images due to the corona discharge products may becomes a large problem.
More specifically, a-Si type light-receiving members have a little lower charging and charge elimination efficiency than other light-receiving members (since the former requires a larger amount of corona charging electric currents in order to obtain the desired charging and charge elimination potential), and hence the charging and charge elimination by corona discharge applied to the a-Si type light-receiving members are carried out while greatly increasing the amount of charging electric currents. This is accomplished by increasing the voltage applied to the corona assembly compared to other light-receiving members.
The a-Si type light-receiving members are mostly used in high-speed electrophotographic apparatus. In such a case, the amount of charging electric currents may reach, e.g., 2,000 .mu.A.
Since the amount of corona charging electric currents is proportional to the quantity of ozone produced, the ozone may be produced in an especially large quantity when the light-receiving member is an a-Si type light-receiving member and the charging and charge elimination are carried out by corona changing. Hence, the faint images or smeared images due to the corona discharge products may become a large problem.
In addition, in the case of the a-Si type light-receiving members, they have a much higher surface hardness than other photosensitive members. Accordingly, any deposits on the light-receiving member can be etched and removed only with difficulty during the step of cleaning or the like, so that the corona discharge products adhered to the surface of the light-receiving member tend to remain.
Accordingly, in conventional cases, a heater for heating the light-receiving member is provided inside the light-receiving member or hot air is blown to the light-receiving member by means of a hot-air blower and the surface of the light-receiving member is heated (to 30.degree. C. to 50.degree. C.) to keep the surface of the light-receiving member dry so that the corona discharge products having adhered to the surface of the light-receiving member can be prevented from absorbing moisture and making the surface of the light-receiving member exhibit a low resistance, to thereby prevent the phenomenon of faint images or smeared images. Such measures have been taken in some cases. Especially in the case of the a-Si type light-receiving members, this heating and drying means is incorporated in the electrophotographic apparatus as an essential means in some cases.
The developing assembly of such an electrophotographic apparatus has a rotary cylindrical developer carrying member internally provided with, e.g., a movable magnet. On this carrying member, a thin layer of a developer, i.e., a toner or a mixture of a toner and a carrier, is formed, and then the developer is electrostatically transferred to a light-receiving member on which an electrostatic latent image has been formed. This system is widely employed. Japanese Patent Application Laid-open No. 54-43037, No. 58-144865, No. 60-7451 and so forth disclose one example of such a system. As developers, a developer containing magnetic particles, i.e., the mixture of a toner and a carrier or a developer containing magnetite or the like in the toner and containing no carrier can be used.
In this system, by the heat from the light-receiving member, the part of the rotary cylindrical developer carrying member facing the light-receiving member expands, so that the distance between the rotary cylindrical developer carrying member and the light-receiving member becomes short at the portion for applying the developer. This makes the electric field therebetween stronger to make it easier for the developer to be transferred. This also allows the portion of the developer carrying member opposite to that portion to have a longer distance between them, so that the electric field becomes smaller to make it more difficult for the developer to be transferred than usual in some cases. As the result, the image density may become high or low due, in part, to the rotational period of the rotary cylindrical developer carrying member. Occurrence of such a phenomenon may cause substantial damage to the quality of an output image of the electrophotographic apparatus. Accordingly, it has been sought to provide a light-receiving member that rather causes faint images nor smeared images even if the light-receiving member is not heated.
In addition, in an electrophotographic apparatus that successively repeats the steps of charging, exposure, development, transfer, separation and cleaning for performing scrape cleaning by means of a blade, such repeated operation may cause a gradual increase in the frictional resistance of the surface of the light-receiving member. An increase in the frictional resistance results in a great reduction of cleaning performance in the removal of residual developer (or toner). If the copying steps are repeated in such a state, fine particles of the developer or those of external additives such as strontium titanate and silica contained in the developer may scatter to adhere to the wire electrode of the corona assembly (hereinafter referred to as "corona assembly wire") to cause discharge non-uniformity. Once the discharge non-uniformity has been caused by the wire contamination of the charging assembly, blank areas in lines, scale-like (or wavy) fog spreading over the whole image, black spots (0.1 to 0.3 mm diameter) locally occurring without periodicity, and the like may occur to cause a great reduction of the quality of output images. Also, once the corona wire contamination has occurred, an abnormal discharge is caused between the contaminated portion and the light-receiving member, so that the surface of the light-receiving member may break to cause faulty images.